(1) Field of the Invention
The present invention relates to a porcelain hollow insulator for transformers, instrument transformers, switches or the like and particularly to improvement of an explosion preventing property of a porcelain hollow insulator for a gas or oil filled insulated bushing.
(2) Related Art Statement
Hitherto, there has been proposed a porcelain hollow insulator as disclosed in Japanese Patent Application Laid-open Publication No. 61-151909. Such a porcelain insulator has a resin lining layer formed on the inner wall surface by spraying a resin by means of a spray nozzle while the hollow insulator is rotated about a fixed longitudinal axis. The resin lining layer is useful to improve safety of the porcelain insulator by preventing the fragments of the insulator from scattering so as not to damage peripheral instruments and/or human bodies when the porcelain insulator is broken by an abnormal high internal pressure caused by an accidental flashover within the insulator or an external force due to an earthquake or the like.
Such conventional porcelain hollow insulators used in the bushings however have not been settled regarding numerical conditions of the adhering force, tensile strength and thickness of the resin layers. Accordingly, there is a problem that some of the porcelain hollow insulators having the resin lining layer do not have a satisfactory explosion preventing property.